Precision Measurements with Polarized Cold Neutron Beams and 3He

使用偏振冷中子束和 3He 进行精密测量

• 批准号: 0244972
• 负责人: Timothy Chupp
• 金额: $ 66万
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-05-15 至 2006-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0244972&HistoricalAwards=false
• 关键词: Precision; Measurements; Polarized; Cold; Neutron

The neutron is a sub--atomic particle thatcomprises more than half of the matter in theworld. Within the nuclei of most atoms, theneutron remains stable, but when freed from thenucleus, it is unstable. Free neutrons are thusan important tool for study ofsub--atomic physics, because the decay andinteractions of free neutrons reveal theinteractions of its constituents and decayproducts. Neutrons also have spin, the quantummechanical property of the most fundamentalpieces of matter that distinguishes two states calledspin--up and spin--down. Spin is responsiblefor the nuclear magnetism exploited, for example,in NMR and MRI. The spin states also affect thedecay and interactions of neutrons, and so thecontrol of neutron spin becomes useful for moredetailed study of sub--atomic interactions. Inthe proposed research, free neutrons produced bya particle accelerator at Los Alamos NationalLaboratory and at the nuclear reactor at NISTwill be used in experiments that control theneutron spin to reveal weak interactions andpossible new physics beyond the Standard Model that summarizes known elementaryparticle interactions.The neutron spins in a beam of neutron will be manipulated byselecting predominantly one spin state with aspin filter based on laser polarized $^3$He. Theneutron spin can be reversed usingmagnetic fields that couple to the nuclearmagnetic moment. Very precise measurement of theneutron polarization ({\it i.e.} the excessfraction of the selected spin state) and precisespin reversal are required to mitigate falseeffects that may arise. The techniques of$^3$He polarization, the spin filter, and spinflipping will be greatly improved as we undertakethese experiments.The objective of the Los Alamos experiment ismeasurement of the weak interaction effects onthe absorption of neutrons by hydrogen. The weakinteractionis characterized by absorption and emission ofparticles that have a handedness that correlatesthe spin orientation with the direction of motion.This handedness allows observation of the weakinteraction amidst the much stronger interactionsof neutrons and protons. Definitive characterization of the weakinteraction between the neutron and proton iscrucial to fully understanding the forces thatbind the nucleus. The experiment at NIST measuresthe dependence of neutron decays on the spinstate. In a dedicated detector, neutron decaysare observed by simultaneously detecting the proton andelectron. Thethird particle emitted, the neutrino, is too elusive todetect with high efficiency. A dependence ofthe electron's and proton's relative motion on the neutron spinstate would reveal interactions that are notsymmetric under reversal of time, a specialsignature that could reveal new physics beyondthe Standard Model, physics that mayexplain the origin of matter in the Big Bang. The advancedtechniques of spin state selection, precisionpolarimetry, and spin flipping will be applied toa planned experiment with the objective of preciselymeasuring the handedness of neutron decays. Whencombined with other neutron decay measurementsthese measurements will also probe physics beyond theStandard Model.This work probes deep intellectual questionsabout the most fundamentalpieces of matter. The aim is to collect datathat will help complete the picture of elementaryparticles and their interactions. The techniqueshave much broader impact. Laser polarized$^3$He and $^{129}$Xe used in related experimentsare now used in biomedical research, materialsscience, and may be applied in advances ofquantum computation. This research is a remarkabletraining ground for undergraduate and graduatestudents. The technical challenges combined withthe deep intellectual issues provide motivationand develop technical skills. Several undergraduates willgain research experience working along with graduate students andsenior researchers. Graduate students emergebroadly capable and move on to prepare forfaculty positions as well as interdisciplinaryresearch. This work has also led to developmentof new courses for non--physics majors and to aset of public lectures on Nuclear Magnets.The theme for the public isthat, in the context of probing fundamentalproblems of physics -- exciting in their ownright, the hardest problems produce the mostinnovative solutions with spin--offs unimaginableat the outset. Atomic clocks, enhanced MRI, andprobing the origin of matter all follow from thecontrol of nuclear magnetism.

中子是一个亚原子粒子，它在世界范围内占一半以上的物质。在大多数原子的核中，theeutron保持稳定，但是当从thecleus释放出来时，它是不稳定的。因此，自由中子是研究对原子物理学的研究的重要工具，因为自由中子的衰减和互相揭示了其成分和衰减生产的互相。中子还具有旋转，这是最基本的物质的量化特性，它们区分了两个称为spin的状态 - up和旋转。 SPIN负责利用的核磁性，例如在NMR和MRI中。自旋状态还会影响中子的theDecay和相互作用，因此中子自旋的控制对于对亚原子相互作用的详细研究很有用。在拟议的研究中，在Los Alamos Natibalaboratoration和Nistwill的核反应堆处产生的自由中子，用于控制ThenEutron Spin的实验，以揭示出较弱的相互作用和可观的新物理学，超出标准模型，这些模型总结了已知的基本粒子相互作用。基于激光偏振$^3 $ HE，主要以一种旋转状态选择一个旋转状态，将通过选择一个旋转状态来操纵中子。可以使用将对核磁矩的磁场逆转来逆转。需要非常精确的测量值（{\ it，即}所选旋转状态的过度分数）和precispin逆转以减轻可能出现的虚假效应。当我们进行实验时，$^3 $ HE极化，自旋滤波器和旋转的技术将大大改善。Los Alamos实验的目的是对弱相互作用对氢对中子吸收的弱相互作用影响的目标。弱互动的特征是粒子的吸收和发射，其手接与运动方向相关的旋转方向。这种手段可以在中子和质子的质子上更强的相互作用中观察到弱互动。中子和质子之间的弱互动的明确表征，以充分理解构成细胞核的力。 NIST测量的实验中子衰变对Spinstate的依赖性。在专用的检测器中，通过同时检测质子和电子观察到的中子脱发。发射的中微子发出的三个粒子过于难以捉摸，效率很高。电子和质子的相对运动对中子旋转状态的依赖性将揭示在时间反转下是不对称的相互作用，这是一种特殊的签名，可以揭示出超出标准模型的新物理学，物理学可以解释大爆炸中物质的起源。旋转状态选择，精确偏度计和自旋翻转的晚期技术将被采用TOA计划的实验，目的是精确地衡量中子衰变的惯用性。当与其他中子衰减测量结果兼容时，测量值还将探测thestandard模型以外的物理学。这项工作探讨了最基本的物质问题。目的是收集Datathat将有助于完成基本粒子及其相互作用的图像。技术避免影响更大。激光偏振$^3 $ He和$^{129} $ XE用于现已用于生物医学研究，材料科学的相关实验中，并且可以用于Quantum Computitation的进步。这项研究是本科生和毕业生的杰出基础。技术挑战与深层智力问题相结合提供了动力，并发展了技术技能。 几位本科生将与研究生和知识研究人员一起工作。毕业生的能力并继续准备福生职位以及跨学科研究。这项工作还导致了针对非物理专业的新课程开发的，并在核磁铁上的公开演讲中浮现。用自旋产生最多的溶液 - 从一开始就没有想象力。原子钟，增​​强的MRI，并探索物质的起源，全部来自核磁的控制。